A conventional, radiation detector, for example, has a single crystal body of CdTe or CdZnTe used for a conversion layer sensitive to radiation. Since these single crystal bodies have wide gaps and are formed of heavy elements, the product can operate at room temperature and has a characteristic of being highly sensitive. However, it is very difficult in production of an ingot to grow a single crystal of large area for two-dimensional imaging. Furthermore, a two-dimensional image detector cannot be produced since material cost of a single crystal body becomes unrealistically high, and a crystal defect in even part of the single crystal body would make it impossible to obtain a pixel in that location.
On the other hand, a polycrystalline semiconductor film of CdTe or CdZnTe formed by the CVD method, PVD method or the like includes many crystal grain boundaries, and is inferior to a single crystal body in electrical and radiation detecting characteristics. In use as a radiation detector for an X-ray area, in order to absorb X-rays, a thickness of several hundred micrometers is needed as thickness of a detecting layer. Even if signal charges are collected from X-ray irradiation by applying a bias voltage to the detecting layer of such thick polycrystalline film, sensitivity and response will fall remarkably due to the generated electric charges being captured by the grain boundaries and the like in the polycrystalline film.
Then, attempts have been made to improve carrier mobility by doping a CdTe or CdZnTe polycrystalline semiconductor film with a halogen such as Cl, thereby to improve detection characteristics with respect to light or radiation of the polycrystalline semiconductor film.
As disclosed in Patent Document 1, for example, a polycrystalline semiconductor film or polycrystalline semiconductor laminated film is formed by vapor deposition or sublimation technique from a source consisting of a mixture of a first material including at least one of CdTe, ZnTe and CdZnTe and a second material including at least one of CdCl2 or ZnCl2. Consequently, the polycrystalline semiconductor film consisting of at least one of CdTe, ZnTe and CdZnTe can be doped with Cl, and the defect level of crystal grain boundaries is protected by Cl, to improve radiation detecting characteristics. With this method, the defect level of crystal grain boundaries in the interior of the polycrystalline semiconductor film can also be protected.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2004-172377